1. Field of the Invention
The present invention relates to apparatus for transmitting and receiving video data in a digital signal, particularly a transmitting apparatus that converts parallel video data into serial video data for transmission.
2. Description of the Related Art
Pictures of high quality have been demanded in recent years, and semiconductor technology that supports their realization has been developed, so that video signals are digitized just as audio signals are digitized, and signal processing and recording are often done in digital form. If video data is processed in digital form, then the transmission of the video data is meaningless unless the transmission is also made in digital form. Particularly, high-quality transmission is required in broadcasting equipment.
Further, in data transmission between pieces of broadcasting equipment, connection between them should be easy. Therefore, data form, signal level, and the like are standardized for transmission between pieces of broadcasting equipment. As an example of the standardization, the SMPTE 260M specifications (See SMPTE 260M "Digital Representation and Bit-Parallel Interface-1125/60 High-Definition System" SMPTE Journal. April, 1992) and others have been provided for HDTV signals.
In the following, as a prior art example, a method of transmitting an video data following the SMPTE 260M specifications, which are provided as a standard of a bit-parallel interface for HDTV signals, is described with reference to FIGS. 2, 6 and 7. FIG. 6 is a block diagram of a transmitter for transmitting video data in HDTV following the SMPTE 260M specifications. FIG. 7 is a block diagram of a receiver. In the transmitter shown in FIG. 6, Y indicates parallel data obtained by digitizing an analog luminance signal (Y). Similarly, Pb and Pr are respectively parallel data obtained by digitizing analog chrominance signals (Pb) and (Pr). The input data Y is multiplexed with synchronizing codes and ancillary data such as audio data during blanking by a Y-channel blanking-data multiplexer 19 to be output as data YD. The input data Pb and Pr are word-multiplexed by a chrominance-data multiplexer 18 and multiplexed with synchronizing codes and ancillary data such as audio data during blanking by a Pb/Pr-channel blanking-data multiplexer 20 to be output as data Pb/PrD, FIG. 2 shows the timing relationship between an analog video signal and corresponding digital video data multiplexed with synchronizing codes and other data. As shown in FIG. 2, one digital line corresponding to one horizontal period consists of a digital effective line of video data and digital line blanking corresponding to horizontal blanking. Further, the first four words (EAV) and the last four words (SAV) of digital line blanking are timing-reference codes containing synchronizing information. Ancillary data such as audio data can be multiplexed in packet form during the period obtained by removing the EAV and SAV periods from the digital blanking period. On the other hand, in a receiver shown in FIG. 7, synchronizing codes arranged in digital line blanking are detected and ancillary data is separated from the received data YD in a Y-channel blanking-data separator 21. Similarly, synchronizing codes are detected and ancillary data is separated from the received data Pb/PrD by a Pb/Pr-channel blanking-data separator 22. Further, video data extracted from the data Pb/PrD is separated into chrominance data Pr and Pb by a chrominance-data separator 23.
The transmission of video data is made possible by the above means specified by SMPTE 260M. However, the implementation requires a great number of signal lines in the transmission channel. SMPTE 260M specifies that twisted-pair cable with individual shields should be used for signal transmission. Therefore, 42 signal lines in the 10-bit system and 34 signal lines in the 8-bit system are needed in addition to ground lines. These lines are of course accommodated in a single compound cable, which is, however, too thick to be handled easily.
Further, as shown in FIG. 2, in a signal specified by SMPTE 260M, an analog-line-blanking signal is replaced by a digital-line-blanking signal. Therefore, information about the horizontal phase and vertical phase in a video signal is placed in the F bit, V bit, and H bit of the EAV and the SAV.
Table 1 shows the composition of the timing-reference signal.
TABLE 1 ______________________________________ Composition of timing-base signal Bit number Word 9 0 Number MSB 8 7 6 5 4 3 2 1 LSB ______________________________________ 1 1 1 1 1 1 1 1 1 1 1 2 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 4 1 F V H P.sub.3 P.sub.2 P.sub.1 P.sub.0 0 0 ______________________________________ F = 0: Period of the first field 1: Period of the second field H = 0: SAV 1: EAV V = 0: The other period 1: Period of field blanking P.sub.0, P.sub.1, P.sub.2, P.sub.3 : Protection bits MSB: Most significant bit LSB: Least significant bit
In particular, as shown in FIG. 8, vertical-phase information should be read from a change in the F bit that occurs once in 1125 lines and a change in the V bit that occurs three times in 1125 lines.
A receiver of a transceiver reads the vertical-phase information from these changes in the V and F bits, so that once an error occurs in either in a V or F bit, errors continue in several lines to tens of lines.
Further, if the vertical phase of an input signal is changed discontinuously by some causes, it takes several lines to tens of lines before a new vertical phase is attained.